1. Field of the Invention
The present invention relates generally to turbines and more specifically to a highly efficient unidirectional turbine that harnesses energy from a fluid flow to produce power.
2. Discussion of Background Information
For many years turbines have been harnessing energy from fluid flow to produce power. Windmills, gyromills, delta turbines and cyclomills have long harnessed energy from wind and converted the same to power. Hydropower turbines harness ocean and tidal currents which are capable of providing a virtually inexhaustible supply of emission-free renewable energy. For example, the Darrieus turbine, a wind turbine, and the Gorlov Helical Turbine (GHT), a water turbine, each take a unique approach to harnessing energy in fluid flow to generate power.
The Darrieus wind turbine, a Vertical Axis Wind Turbine (VAWT), comprises vertical airfoils affixed in a symmetric arrangement to a vertical shaft. The vertical shaft connects to a gear box and generator for converting torque to power. Although effective for harnessing wind power from air flowing from any direction, this VAWT presents several disadvantages. First, the Darrieus turbine fails to self start and requires some initial force to begin rotating in a current. Second, the airfoils produce maximum torque at two points in their rotation cycle, the two points at which the airfoils are perpendicular to direction of airflow. The Darrieus turbine airfoils thus present a varying angle of attack in relation to current, and this leads to a sinusoidal fluctuation in resultant torque that creates a potentially destructive resonance at a natural frequency of the hydrofoil blades. The Darrieus turbine therefore requires some sort of braking mechanism for slowing rotation of the VAWT prior to destructive resonance. Lastly, the shaft of the Darrieus turbine couples with a generator requiring gearing multiplication and that gearing presents yet another potential mode of mechanical failure.
The GHT is a water based turbine based in principal on the Darrieus turbine in that airfoil shaped blades run along a center shaft and axis of rotation. The design of GHT, however, addresses some of the deficiencies of the Darrieus turbine. First, the hydrofoil blades of the GHT twist about the axis of rotation in a helical pattern such that the blades present a constant, optimal angle of attack within a current. This eliminates the resonance issue associated with the Darrieus turbine. Second, the GHT requires minimal gearing multiplication between the turbine and power generator. Despite these improvements, the GHT, however, presents some constraints. GHT efficiency is measured up to only about 35%. Also, because the helical configuration of blades sweeps a circumference of right cylinder, large centrifugal stresses develop. The GHT generally requires containment and constraint within a structure having an inflow and outflow channel preferably including inwardly extending, contoured sidewalls for guiding fluid flow and reducing turbulence.
U.S. patent application Ser. No. 11/985,971, incorporated herein by reference, addresses some of these issues. In that application, two or more spiral wound blades form a barrel shaped turbine that efficiently harnesses fluid flow for the generation of energy. That turbine comprises radial spokes that anchor each of the two or more spiral wound blades to a central shaft of the turbine. The radial spokes and central shaft potentially create drag and potentially accumulate debris, such as seaweed, which also may reduce efficiency. Furthermore, in certain embodiments, the configuration of spokes may address deflection issues insufficiently because the two or more blades are independently anchored to the central shaft, thereby preventing any load transfer between the active and non-active blades.
Because ocean and tidal currents exist everywhere in the world and either flow constantly or at an extremely predictable rate of change, converting the energy in these currents to electricity could provide a predictable, reliable supply of electricity to electric power systems in many parts of the world. Approximately seventy percent (70%) of the population of the entire world lives within two hundred miles of an ocean, making that an accessible source of renewable energy. Accordingly, a need exists in the art for an easily produced, sturdy, highly efficient turbine that produces high power output at low speeds and efficiently harnesses energy from a wide range of sites and water flow conditions including, tidal currents, open ocean currents, rivers, causeways, canals, dams and any other natural or manmade water flow.